@Gav
You are not the first one having the same MUI problem. For me it worked from first time, I am using it on Pegasos though and all my libraries etc. are up to date. Thats whats probably happening, you have something that JW uses and it's too old version. I checked the docs and here are the classes I am using:
NList.mcc 20.111
Textinput.mcc 29.5
MailText.mcc NONE(!)
I seem to miss mailtext.mcc eventhough its mentioned in docs.. well as long as it works :-)